This invention relates to enclosed manually operable electric switching apparatus commonly referred to as disconnect or safety switches. More specifically, this invention pertains to an enclosed switching apparatus of the aforementioned type which has two switching devices mounted within a common enclosure, both switches being controlled by a single handle, double-throw operating mechanism. Switching apparatus of this type is commonly used to alternatively connect one of two load devices to a source of electric power or to connect a singular load device alternatively to one of two separate sources of electric power. In either of the foregoing applications of such switching apparatus it is essential that only one of the switching devices be operated to an ON condition at any given period of time and that the other switching device remain in its OFF condition during that time.
U.S. Pat. No. 4,034,170 issued July 5, 1977 to R. D. Raabe et al discloses electrical transfer switching apparatus of the aforementioned type. The double-throw operating mechanism of that apparatus has a single slide member driven in alternate opposite directions by the handle. The single slide is connected to each switch device by respective operating levers of the switch devices. The single slide arrangement requires that the operating levers be mounted in reverse orientation with respect to each other to achieve the desired operation for the apparatus. Such reverse orientation requires that clearance space for lever movement be provided within the enclosure both fore and aft of the rotational axes of the switch devices, thereby establishing a certain minimum depth for the enclosure. Moreover, the single slide arrangement disclosed in Raabe et al is provided with alternative connection slots for the switch device operating levers for reverse operation of the switch devices. Accordingly, particular attention need be given during assembly of the apparatus to ensure that the operating levers are in fact mounted in reverse orientation since connection thereof to the slide in an improper orientation is possible and would result in both switch devices being operated to the ON condition at the same time.
In applications where the aforementioned type of switching apparatus is utilized as a fusible transfer switch to alternatively connect a load between two sources of electric power, the electric power sources are usually connected to the switch devices through the respective fuses. In such arrangement, the fuses remain electrically hot even when both switch devices are in their OFF condition. In such application the National Electric Code requires two single-throw (non-fusible) safety switches be mounted adjacent to the fusible transfer switch and connected between the respective source and fuses for each of the two sources to permit power to be disconnected from the fuses when servicing the same.